1,324 research outputs found
Neutrino masses in RPV models with two pairs of Higgs doublets
We study the generation of neutrino masses and mixing in supersymmetric
R-parity violating models containing two pairs of Higgs doublets. In these
models, new RPV terms arise in the
superpotential, as well as new soft terms. Such terms give new contributions to
neutrino masses. We identify the different parameters and
suppression/enhancement factors that control each of these contributions. At
tree level, just like in the MSSM, only one neutrino acquires a mass due to
neutrino-neutralino mixing. There are no new one loop effects. We study the two
loop contributions and find the conditions under which they can be important.Comment: 22 pages, 5 figures, 3 appendice
The two-photon exchange contribution to muonic hydrogen from chiral perturbation theory
We compute the spin-dependent and spin-independent structure functions of the
forward virtual-photon Compton tensor of the proton at one loop using heavy
baryon effective theory including the Delta particle. We compare with previous
results when existing. Using these results we obtain the leading hadronic
contributions, associated to the pion and Delta particles, to the Wilson
coefficients of the lepton-proton four fermion operators in NRQED. The
spin-independent coefficient yields a pure prediction for the two-photon
exchange contribution to the muonic hydrogen Lamb shift, eV. We also compute the charge, , and Zemach, , moments for .
Finally, we discuss the spin-dependent case, for which we compute the
difference between the four-fermion Wilson coefficients relevant for hydrogen
and muonic hydrogen.Comment: 43 pages, 6 figures. Minor corrections, references added, misprints
corrected, Eq. (3.19) added, results unchanged. To meet journal versio
The Lamb shift in muonic hydrogen and the proton radius from effective field theories
We comprehensively analyse the theoretical prediction for the Lamb shift in
muonic hydrogen, and the associated determination of the proton radius. We use
effective field theories. This allows us to relate the proton radius with
well-defined objects in quantum field theory, eliminating unnecessary model
dependence. The use of effective field theories also helps us to organize the
computation so that we can clearly state the parametric accuracy of the result.
In this paper we review all (and check several of) the contributions to the
energy shift of order , as well as those that scale like
logarithms in the context of non-relativistic effective field
theories of QED.Comment: 34 pages, 8 figures, 1 table, 1 appendix. Minor corrections,
references added. Replaced to meet journal versio
Model-independent determination of the two-photon exchange contribution to hyperfine splitting in muonic hydrogen
We obtain a model-independent prediction for the two-photon exchange
contribution to the hyperfine splitting in muonic hydrogen. We use the relation
of the Wilson coefficients of the spin-dependent dimension-six four-fermion
operator of NRQED applied to the electron-proton and to the muon-proton
sectors. Their difference can be reliably computed using chiral perturbation
theory, whereas the Wilson coefficient of the electron-proton sector can be
determined from the hyperfine splitting in hydrogen. This allows us to give a
precise model-independent determination of the Wilson coefficient for the
muon-proton sector, and consequently of the two-photon exchange contribution to
the hyperfine splitting in muonic hydrogen, which reads meV. Together with the
associated QED analysis, we obtain a prediction for the hyperfine splitting in
muonic hydrogen that reads meV and
meV. The error is dominated by the
two-photon exchange contribution.Comment: 18 pages, 4 figures, 3 tables. v2: Minor corrections to meet journal
version, references adde
P-wave heavy quarkonium spectrum with next-to-next-to-next-to-leading logarithmic accuracy
We compute the heavy quarkonium mass of (angular momentum) states,
with otherwise arbitrary quantum numbers, with next-next-to-next-to-leading
logarithmic (NLL) accuracy. This constitutes the first observable in heavy
quarkonium for which two orders of the weak-coupling expansion sensitive to the
ultrasoft scale are known and the resummation of ultrasoft logarithms is made.
We also obtain, for the first time, resummed NLL expressions for the
different fine and hyperfine energy splittings of these states, which are not
sensitive to the ultrasoft scale but still require resummation of (hard)
logarithms. We do this analysis for the equal and non-equal mass cases. We also
study an alternative computational scheme that treats the static potential
exactly. We then perform a comprehensive phenomenological analysis: we apply
these results to the , bottomonium, and charmonium systems and
study their convergence.Comment: 49 pages, 15 figures, 1 tabl
Current and future perspectives of positronium and muonium spectroscopy as dark sectors probe
Positronium and Muonium are purely leptonic atoms and hence free of an
internal sub-structure. This qualifies them as potentially well suited systems
to probe the existence of physics beyond the Standard Model. We hence carry out
a comprehensive study of the sensitivity of current Positronium and Muonium
precision spectroscopy to several new physics scenarios. By taking properly
into account existing experimental and astrophysical probes, we define clear
experimental targets to probe new physics via precise spectroscopy. For
Positronium we find that, in order for the spectroscopy bounds to reach a
sensitivity comparable to the electron gyromagnetic factor, an improvement of
roughly five orders of magnitude from state-of-the-art precision is required,
which would be a challenge based on current technology. More promising is
instead the potential reach of Muonium spectroscopy: in the next few years
experiments like Mu-MASS at PSI will probe new regions of the parameter space
testing the existence of medium/short range (MeV and above) spin-dependent and
spin-independent dark forces between electrons and muons.Comment: 8 pages, 6 figures. Version changed to match journal version. Figures
update
Reseñas
Antonio REY GONZÁLEZ, Estudios médico-sociales sobre marginados en la España del siglo XI
Autonomía y libertad de Cátedra. Dos siglos de historia universitaria
Nombrado Doctor Honoris Causa en el acto de apertura del día 2 de octubre de 200
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